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Innate immune reactivity to dental alloys

Rachmawati, D.

2016

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citation for published version (APA)Rachmawati, D. (2016). Innate immune reactivity to dental alloys.

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CHAPTER 5

Immunostimulatory capacity of dental casting alloys on endotoxin responsiveness

Dessy Rachmawati1,2,1 B. Mary E. von Blomberg1, Cornelis J. Kleverlaan3,

Rik J. Scheper1, Ingrid M.W. van Hoogstraten1,

1 Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands 2Department of Dental Biomedical Science, Faculty of Dentistry, University of Jember, Indonesia

3 Department of Dental Materials Science, Academic Center for Dentistry Amsterdam (ACTA), VU University Amsterdam and University of Amsterdam, The Netherlands

This article is being submitted

92 IMMUNOSTIMULATORY CAPACITY OF DENTAL CASTING ALLOYS

ABSTRACT

Statement of problem. Oral metal exposure has been associated with systemic and local adverse reactions, putatively due to elemental release from the alloys. It has been shown that supra-physiological concentrations of salts from dentally applied metals can activate innate cells via TLR4 (Ni, Co, Pd) and TLR3 (Au). It is, however, still unknown whether direct exposure to the solid alloys can also trigger or affect innate immune reactivity.

Purpose. Here we questioned whether dental cast alloy specimens can activate innate cells and influence their responsiveness to bacterial endotoxin.

Material and methods. Human MoDC and THP-1 cells were cultured on top of 8 different metal alloy specimens or in alloy exposed culture medium, in the presence or absence of endotoxin (LPS). IL-8 production was evaluated after 24 hrs of culture.

Results. Dental cast alloys induced IL-8 production in MoDC and THP-1 cells, with Au and Pd-Cu alloy specimens providing the strongest stimulation. When testing alloy exposed culture media, these turned out to contain sufficient stimulatory metal ions to induce detectable IL-8 production in THP-1 cells, except for the Ni-Cr and stainless steel exposed medium. Au and Pd-Cu alloys were most effective, also in potentiation of LPS responsiveness, as measured by IL-8 production.

Conclusions. Using an in vitro culture system for exposure of MoDC and THP-1 cells to different metal specimens we showed for the first time that contact with the solid alloys, in particular when containing Pd or Au, can trigger innate immune responses and augment the host’s responsiveness to bacterial endotoxin.

IMMUNOSTIMULATORY CAPACITY OF DENTAL CASTING ALLOYS 93

5

INTRODUCTION

The oral cavity is a port of entry for early infections, many Gram-positive and negative bacteria contribute to dental plaque around the teeth and colonize the mucosal surface. Balancing the inflammatory reactions to effectively fight pathogenic invaders without too much damage is of major importance. Here we studied in how far the presence of dental cast alloys in the oral cavity can affect innate responsiveness against bacteria.

Previously we investigated the immune stimulatory capacity of nickel (Ni), cobalt (Co) and other transition metals in the form of metal salt solutions. In these studies Ni, Co and palladium (Pd) were shown to activate monocyte derived dendritic cells (MoDC) via binding to TLR4, gold (Au) predominantly via TLR3, whereas copper (Cu) and mercury (Hg) activated innate cells via still unknown mechanisms(Rachmawati et al. 2013; Rachmawati et al. 2015). Low, near physiological metal ion concentrations, as can be found in the blood, did not activate innate cells, but could potentiate endotoxin responsiveness of THP-1 cells, a cell line used as a model for innate immune reactivity (Rachmawati et al. 2016). The local concentrations of metal salts in the oral cavity, in particular in the immediate vicinity of metal reconstructions, may, however, exceed these physiological plasma levels.

Conditions in the oral cavity, created by a.o. temperature, microbiota, pH, saliva, exogenous agents like tobacco and alcohol, ongoing immune reactions, the combination of different metals as well as the shape and surface treatment of the dental alloys, may allow for increased corrosion and subsequent metal ion release (Chaturvedi 2013; Milheiro et al. 2015) For this reason studying the effects of metal salt solutions was considered most relevant by us and most other investigators(Milheiro et al. 2014; Elshahawy et al. 2009), and as a consequence, the direct effects of the different dentally applied alloys on innate immune cells received little attention, so far.

To study the effects of dental alloys on innate cells in vitro, we have chosen the most frequently used alloys (Table 1) and as innate responder cells ex vivo human MoDC as well as the THP-1 cell line, since a cell line would be more convenient for future large scale screening studies. We cultured the cells on top of the alloy specimens in 24 wells culture plates, as well as in alloy exposed culture medium to check whether potential effects are due to the release of metal ions. As a read out we evaluated IL-8 production in the culture supernatants after 24 hrs. Since the pathogenic role of Gram negative bacteria in the oral cavity, such as in subgingival plaques(Matto et al. 1996) and periodontitis (Dai et al. 2014; Jain and Darveau 2010; Siqueira, Jr. and Rocas 2007) is of major importance, we used the endotoxin LPS to represent bacterial innate stimulation. LPS is a powerful innate stimulant acting via ligation of TLR4(Raghavan et al. 2012) and represents the major PAMP molecule produced by Gram-negative bacteria.


The present study questions: 1) in how far different dental cast alloys can trigger innate responsiveness in MoDC and in THP-1 cells as a model and 2) whether these cast alloys or the low levels of metal ions released from them, can interfere with the endotoxin responsiveness of these cells.

Table 1. Alloys selected for this study

106

Table 1. Alloys selected for this study

No Material Manufacturer Composition Usage

1 Acrylate (methyl methacrylate)

GC Europe N.V, Leuven Belgium

- Copolymer of methylmetharylate & diethyl phtalate, polymethylmethacrylate (powder)

- Methyl methacrylate & N.N-dimethyl-p-toluidine (liquid)

Temporary crown and bridge resin

2 Ni-Cr alloy Noritake Dental Supply, Japan

Ni 62%, Cr 19.1%, Mo 7.1%, Ga 2%

Metal-ceramics restorations

3 Co-Cr alloy Brident International, USA

Co 63%, Cr 27%, Mo 6%, Other 4%

Partial denture alloy

4 Pd-Cu alloy (Orion Vesta)

Elephant Dental B.V., Hoorn, Netherlands

Au 2%, Pd 78.9 %,Cu 10%,Ga 9 %, Ir < 1 %

Metal-ceramics restoration

5 Pd-Ag alloy (Orion Argos)


Au 0.1 %, Pd 53.3 %, Ag 36.3 %, Sn 7 %, In 2 %, Zn < 1 %


6 Ti (Ti-6Al-4V) Straumann AG, Basel

Al 6% and V 4% Implant, crown, bridges

7 Amalgam (Cavex non Gamma-2)

Cavex Holland BV, Netherlands

Hg 50%, Ag 22-32%, Sn14%, Cu 8%, and other trace metals

Fillings

8

Au alloy (Degudent G) (Pd free)


Au 86%, Pt 11.5%, Zn 1.6 % In, Rh, Fe each < 1%


9 Stainless steel Dentaurum, Germany

Fe 69.35%, Ni 10%, Cr 17%, Mo 2-4%, Si 1%

Pediatric crown Orthodontic braces

innate stimulant acting via ligation of TLR4(Raghavan et al. 2012) and represents the major

PAMP molecule produced by Gram-negative bacteria.

The present study questions: 1) in how far different dental cast alloys can trigger innate

responsiveness in MoDC and in THP-1 cells as a model and 2) whether these cast alloys or the low


5

MATERIALS AND METHODS

MoDC culture

MoDC were generated from freshly prepared PBMC as previously described. Briefly(Bontkes et al. 2002), adherent monocytes were cultured for 6-7 days in a humidified incubator in 10 ml IMDM medium (Biowhittaker, Verviers, Belgium) supplemented with 10% heated-inactivated foetal calf serum (FCS; Hyclone, Logan USA), 0.1 mg/ml streptomycine (Invitrogen), 100 IU/ml Na-penicilline G (Invitrogen), 1% L-glutamine 200 mM (Merck, Darmstadt, Germany), and 1% β-mercaptoethanol, 1000 U/ml granulocyte-macrophage colony stimulating factor (GM-CSF Novartis, The Netherlands) and 20 ng/ml IL-4 (R&D systems lot AG270911A). After 6-7 days, immature dendritic cells (iDC) were harvested and seeded on the surface of different dental cast alloys in the 24 well flat tissue culture plates (Cellstar Greiner Bio-One; 25.104

cells/well in a final volume of 1ml).

THP-1 cells

A vial of cell passage 17 of THP-1 cells (ATCC, Rockville, USA) was kept at -80°C until thawing. The cells were cultured in 75cm2 culture flasks (Cellstar Greiner Bio-One) at a density of 106 cells /1 ml of RPMI 1640 (Biowhittaker, Verviers, Belgium) containing 1% L-glutamine 2 mM (Merck, Darmstadt, Germany), 0.1 mg/ml streptomycine (Invitrogen),100 IU/ml Na-penicilline G (Invitrogen) and 10% heat-inactivated foetal calf serum (FCS: Hyclone, Logan USA). The THP-1 cells were maintained in logarithmic growth by passaging every 3-4 days. The THP-1 cells were seeded on the surface of different dental cast alloys in the 24 wells plate (flat bottom, Greiner Bio-One) in a concentration of 25.104 cells per well. The THP-1 cells were then exposed for 24 hrs in a final volume of 1ml.

Alloy specimen preparation

8 different dental cast alloys were used in this study (table 1). Each alloy was formed in diameter 10 mm and 1 mm thickness. Alloys were made by the lost-wax casting process. First, a wax model was made, wax was removed, and castings of alloys were performed. Cooling and finishing were done according to the manufacturer’s instructions. Specimens were finished and polished using finishing stone burs. All processes of finishing and polishing were carried out in a similar way to simulate the preparation of the cast metal alloys for clinical cases. As a non-metal control, acrylate disks were used (GC tempron, GC Europe N.V, Leuven, Belgium).

Exposure to dental cast alloy and LPS

The specimens were rinsed in a detergent solution for 5 minutes, scrubbed and rinsed under tap water and distilled water for 5 minutes. The specimens were then dried and placed in 70% ethanol and sterilized in an autoclave (125°C for 60 minutes). At the day of culture these were placed on the bottom of 24 well plates in 500 µl culture medium with 25.104


MoDC or THP-1 cells per well, placed on top of the specimens in a final volume of 1ml. Cultures were performed in the absence or presence of LPS (E.coli 055:B5; Sigma-Aldrich, St. Louis, MO, USA). Plates were incubated at 37˚C in 5% humidified CO2. Stimulation by LPS was chosen to be moderate (low dose of LPS chosen), to allow for the evaluation of both stimulation and inhibition by the alloys: for MoDC 0.5 ng LPS/ml and for THP-1 50 ng LPS/ml. Plates were incubated at 37˚C in 5% humidified CO2. After 24 hours, supernatants were collected and stored at -20˚C until measurement. To confirm whether cell activation is due to metal ion release, we also evaluated alloy supernatants obtained by submerging alloy specimens in 500 µl of culture medium (24 well plates; 24 hrs; 37°C). Supernatants (i.e. alloy exposed culture media) were retrieved and stored under sterile conditions.

Dental casting alloy toxicity experiments

In order to measure viability of the cells MTT reduction tests (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (Sigma, St Louis, MO, USA) were used. Approximately 500 µl of cells (25.104/well) were plated in 24 well culture plates and exposed to 500 µl cast alloys supernatants. After 24 hours incubation supernatants were removed and 500 µl of MTT solution (5 mg/ml) was added per well. MTT solution was prepared freshly and dissolved with H2O, filtered through a 0.22-µm filter. The plates were incubated in the dark at 37˚C. After 2-3 hours of incubation, 500 µl DMSO (Merck, Darmstad, Germany) was added to each well and after shaking, the solution was measured using an ELISA reader at OD (optical density) 490 nm. The OD of the cells in the absence of metal was considered as 100%. Viabilities of exposed cells were determined by the formula: OD experimental sample/OD of control cells) x 100%.

IL-8 evaluation

IL-8 production was measured in cell culture supernatants by Enzyme-linked immunosorbent assay (ELISA) with Peli-Kine ELISA kits (Sanquin, Amsterdam, The Netherlands) using 96-well microtiter plates (Nunc maxisorp microtiter plates, Nalge Nunc international), as per the manufacturer’s instructions. Absorbance was measured at 450 nm. The IL-8 concentration in the supernatant was assessed by using calibration curves (lower detection limit: 15.4 pg/ml) and is expressed in pg or ng per ml.

Data analysis

Data is presented as median of at least 5 independent experiments and the interquartile range (25th to 75th percentile). The statistical significance of the effects of various casting alloys on the secretion of IL-8 was analysed by using the non-parametric Wilcoxon rank sum test. All statistics were performed by MedCalc software (Mariakerke, Belgium). P≤0.05 was considered statistically significant.


5

RESULTS

Dental cast alloys induce IL-8 production in MoDC and THP-1 cells.

To study immune stimulatory effects of dental cast alloys on innate cells, first the cytotoxicity of 8 commonly used dental cast alloys (Table 1) for innate cells was determined after 24 hrs of culture. The viability of both MoDC and THP-1 exceeded 80% in all alloy cultures, indicating that these alloys were not toxic to the cells (data not shown). Then MoDC and THP-1 cells were exposed to specimens of these 8 alloys as well as to acrylate, as a non-metal control, and to LPS as a positive control. IL-8 secretion was evaluated in the supernatants after 24 hrs. As shown in Fig.1a, all dental cast alloys induced significant (Wilcoxon p<0.01) IL-8 production in MoDC, whereas acrylate specimens did not. Au alloy provided the strongest stimulus, but potential differences between the metal specimens did not reach statistical significance.

In order to further confirm the innate stimulatory capacity of cast alloys, using the same approach, THP-1 cells were studied (Fig 1b). Although overall IL-8 production levels were lower, robust production of IL-8 could be observed for most alloys which tended to be highest for Au and Pd-Cu alloys, supporting the earlier data. Further experiments were carried out to investigate whether the activation of THP-1 cells resulted from metal ion release into the supernatant or from direct cell contact with the alloys. Therefore alloy exposed medium samples were prepared by submerging the alloys in culture medium for 24 hrs, and evaluated for their stimulatory capacity. For most alloys the supernatants contained sufficient stimulatory metal ions to induce significant, beit low, IL-8 production. However, for Ni-Cr and stainless steel specimens, metal ion release under the present test conditions was apparently too low to activate THP-1 cells (Fig 1c). Again Au and Pd-Cu specimens stood out in most distinct innate immune triggering capacity.

Effects of cast alloys on LPS responsiveness

To evaluate whether cast alloys might affect the host’s reaction to bacterial TLR ligands such as endotoxin, LPS responsiveness of MoDC and THP-1 was evaluated in the presence of the 8 dental alloys. Figure 2a shows that LPS-induced IL-8 secretion by MoDC was significantly higher in the presence of gold alloy specimens, suggesting at least an additive effect of the stimuli. For the other alloys significant potentiation of the LPS response by MoDC was not reached. In THP-1 cells (Figure 2b), on the other hand, where the LPS response in itself is relatively low, significant increments of the LPS induced IL-8 secretion were observed not only with specimens of the Au alloy, but also with Pd-Cu, Pd-Ag, Ti and Amalgam specimens. In addition, supernatants collected from alloys submerged in culture medium were tested for their capacity to potentiate LPS responsiveness of THP-1 cells. As can be seen in Figure 2c, Pd-Cu as well as Au alloy supernatants induced significantly increased LPS induced IL-8 secretion, whereas the other alloys did not increase LPS responsiveness significantly.


5

Figure 1. MoDC (a) and THP-1 cells (b) were exposed to cast alloys. Additionally, THP-1 cells were cultured in alloy-exposed culture medium, called ‘sup’ (c). After 24 hrs of cell culture, IL-8 production was determined. IL-8 concentration is shown in ng/ml for MoDC and in pg/ml for THP-1 (median and interquartile range of 5 independent experiments). P-values are given for significantly different IL-8 production (p<0.05) between alloy exposure and medium control.


5


Figure 2. MoDC (a) and THP-1 cells (b) were exposed to cast alloys. Additionally THP-1 cells were cultured in alloy exposed culture medium, called ‘sup’ (c). All cultures were with or without supplementary low doses of LPS (0.5ng/ml for MoDC and 50ng/ml for THP-1). IL-8 production (ng/ml for MoDC and pg/ml for THP-1) was measured in supernatants after 24 hrs of exposure. The grey columns indicate IL-8 production induced by alloys in combination with LPS, white columns show IL-8 production induced by alloys alone. P-values are given only for significant (p<0.05) effects on LPS induced IL-8 production by alloy exposure as compared to medium control. For clarity medium and acrylate data are shown in both panels.

DISCUSSION

Exposure to metals can have adverse health effects, depending on their concentration and chemical form (Martin et al. 2011). As reported earlier, salts from several dentally


5

applied metals can activate the innate immune system. Here, for the first time, the immune stimulatory effects of alloy specimens on innate cells are demonstrated. The results shed a new light on clinical and experimental experiences with these metals which are notorious for their capacity to activate both innate and adaptive immune responses.

In the present study we tested dental cast alloys as solid specimens, reflecting the actual situation in the oral cavity. An alloy is a mixture of at least two metals, and dental alloys usually contain at least four metals, and often six or more. More than 25 elements in the periodic table of elements can be used in dental alloys including Zn, Hg, Ni, Cu, Co, Au, Pd, Pt, Ag, Ti and Fe (Wataha 2000). The present study was set up to explore in how far commonly used cast alloys can trigger innate responsiveness in MoDC and in model THP-1 cells. The results fit with our earlier findings that most metals used for dental alloys show innate stimulatory activity (Rachmawati et al. 2015; Rachmawati et al. 2013). But, strongest and consistent IL-8 release was found with Au and Pd-Cu containing alloys. These findings might explain why oral exposure to these metals has been associated with distinct clinical problems (Muris et al. 2014).

The stimulatory capacity of dental cast alloys could result from metal ion release, but also from direct contact between the innate cells and the alloys. Several in vitro studies, listed in Table 2 have been reported on the ion release from alloys with largely varying results, depending on the duration of exposure, the method of evaluation, the pH, as well as on the brand, the composition and the surface treatment of the alloy (Elshahawy et al. 2013; 2003). A recent review of (Mikulewicz et al. 2014) summarized the in vivo studies in which metal release was evaluated in clinical fluids. The huge variation in reported metal ion release data stresses the importance of testing the actual alloys themselves, instead of only their salt solutions, for immune stimulatory capacities. In none of these metal ion release studies, the most effective innate stimulatory dose, as assessed in our previous studies, i.e. ranging from 125-750 μM for most metals and 250-750 nM for Hg (Rachmawati et al. 2013; Rachmawati et al. 2015) was reached. It is therefore remarkable that in the present experiments for 6 out of 8 alloys the concentration of metal ions released into plain culture medium within 24 hrs appeared to be high enough to induce significant IL-8 production by THP-1 cells, in particular for Pd and Au based alloys. Actually direct contact of innate cells with the alloys might also contribute to the innate activation, especially in the case of stainless steel and Ni-Cr alloy.Stainless steel does trigger innate responses in both MoDC and THP-1, most likely because of the Ni content (13-15%). Indeed Ni was reported to be released from stainless steel (Table 2). However, in the present study, stainless steel nor the Ni-Cr alloy did release detectable stimulatory ions in the supernatant within 24 hours and also did not potentiate LPS responsiveness. In vivo conditions facilitating metal corrosion could, however, still result in increased Ni ion release and subsequent innate immune reactions. In dentistry, stainless steel crowns are commonly used for brackets and for treatment of primary teeth in children,


to prevent further decay until replacement by permanent teeth. In general, stainless steel is cost-effective to use since it will be removed naturally when the permanent teeth are approaching. The present in vitro results suggest that stainless steel can, however, stimulate inflammation by direct contact with mucosal innate cells. This would be in line with the incidental finding of local gingival inflammation at the site of oral stainless steel exposure, especially in nickel allergic individuals (Pazzini et al. 2011).

Acrylate specimens have been used as a putative negative control, since it is a non-metal material. It has been widely used in dentistry because of its low cost, ease of use and diversity of indications. In agreement with our hypothesis, the results show that direct cell contact with acrylate does not stimulate innate cells.

In a previous study on the innate stimulatory capacity of low, near physiologic metal concentrations, we showed that such low concentrations did not directly activate innate cells but could potentiate LPS responsiveness (Rachmawati et al. 2016). Here we showed that in vitro exposure to most of the alloy specimens also potentiated the inflammatory response to bacterial endotoxin (LPS). This was most obvious with the THP-1 cell line as responder cells, since the basal LPS response of these cells is relatively low as compared to MoDCs. However, under the present, ‘non-corrosive’ conditions, only Pd-Cu and Au alloys did release enough metal ions in the supernatant within 24 hrs to potentiate LPS responsiveness. In aggregate, the present results suggest that the presence of in particular Pd an Au based dental alloys might facilitate anti-microbial immune responses, but also lead to untoward local reactivity perceived as irritancy.

The use of actual dental cast alloys in in vitro studies, instead of metal salt solutions, provides an effective strategy to study potential immune stimulatory effects of orally applied metals. A major advantage of using alloy specimens in such a screening test is that the capacity to release metal ions into the environment is also taken into account. Although generally lower amounts of IL-8 are being produced than by MoDC, THP-1 cells are ideal responder cells in such a test system, in particular for studying effects of metal alloys on LPS responsiveness.

In conclusion, using an in vitro culture system for exposure of MoDC and THP-1 cells to different dental alloys, the present study shows that these alloys, in particular when containing Pd or Au, can trigger innate immune responses and strengthen the host’s responsiveness to bacterial endotoxin.


5

ACKNOWLEDGEMENT

The author would like to acknowledge Prof. Dr. Albert Feilzer for critical review of the manuscript and for stimulating discussions. This study was supported by The Ministry of Research, Technology and Higher Education of The Republic of Indonesia.


Table 2. Reported metal ion release in vitro from dental equipment and alloys

118

Table 2. Reported metal ion release in vitro from dental equipment and alloys Metal

Type of alloy

Methods & conditions of exposure a) Release Reference b)

(name/brand) device / specimen quantification

fluid volume

duration

μg/cm2

ppb (μg/L)

(nM)

Ti Ti–6Al–4V Zimmer (Sulzer Orthopedics)

dental implant Ø 22 mm x 2mm

MEM c) 100ml

28 days

n.d. d) n.d. n.d. (Höhn S and Virtanen S 2015)

Ti (Ormco)

20 orthodontic brackets 4 buccal molar tubes

MEM

30 ml 30 days

? 5.4 114.89 (Ortiz et al. 2011)

Cr Ni-Cr (Remanium CS)

cast alloy specimen Ø 5mm x 3mm

artificial saliva 11.5ml

60 days

0.01 0.8 15.38

(Oyar et al. 2014)

Ni-Cr (Vera Bond II)

cast alloy specimen + electrolysis 40x20x3mm

artificial saliva 50ml

2 days

0.17 66.5 1279 (Galo et al. 2012)

Co-Cr-Mo (Wironit ®)

cast alloy specimen Ø 8mm x3.2mm

artificial saliva pH7.5 artificial saliva pH4 5ml

6 weeks

1.52 1.80

550.0 650.0

10577 12500

(Dimic Ivana D et al. 2014)

Co-Cr (Remanium)



2 days

0.10 37.9 728.84 (Galo et al. 2012)

Stainless steel (Ultraminitrim, Dentaurum)

20 orthodontic brackets 4 molar tubes

MEM 30ml

30 days

? 9.0 173 (Ortiz et al. 2011)

Stainless steel (Preform arch wires, Ortho-Organizers)

orthodontic wire 0.017 × 0.025 inch 100 mm length

Artificial saliva 100ml

28 days 0.51 11.0 211.53 (Gopikrishnan et al. 2015)

Stainless steel (American Orthodontics, 3M Unitek)

2 orthodontic wires 20 ortho brackets 2 ligatures

artificial saliva flow, 0.5ml/min 19.41 L (flow)

28 days

? 0.3 5.76

(Mikulewicz et al. 2014)

Co Co-Cr-Mo (Wironit ®)


artificial saliva pH7.5 artificial saliva pH4 5ml

6 weeks

1.74 4.04

630.0 1460.0

10678 24746

(Dimic Ivana D et al. 2014)

Co-Cr (Remanium)



2 days

0.02 9.3 157.62

(Galo et al. 2012)

Stainless steel (Ultraminitrim, Dentaurum)


MEM 30ml

30 days

? 1.4 23.72 (Ortiz et al. 2011)

Ni-Cr (Remanium CS)

cast alloy specimen Ø 5mm x 3mm


60 days

0.28 21.1 358 (Oyar et al. 2014)

Ni Ni-Cr (Remanium CS



60 days

1.10 82.9

1381 (Oyar et al. 2014)

Ni-Cr (Vera Bond II)



2 days

0.53 207.0 3.45 (Galo et al. 2012)

Stainless steel (Ultraminitrim,Dentaurum)


MEM 30ml

30 days

? 417.0 6.95 (Ortiz et al. 2011)

Stainless steel (Preform arch wires, Ortho-Organizers)

orthodontic wire 0.017 × 0.025 inch 100 mm length

Artificial saliva 100ml

28 days

0.28 6.0 100

(Gopikrishnan et al. 2015)

Stainless steel (American Orthodontics, 3M Unitek)


artificial saliva flow, 0.5ml/min 19.41 L

28 days

? 1.0 16.66


Cu Stainless steel (American Orthodontics, 3M Unitek)


artificial saliva flow, 0.5ml/min 19.41 L

28 days

? 1.6 25.39


Pd-Cu (Orion Vesta)

cast alloy specimen 2.06cm2

lactic acid/NaCl; pH2.3 5ml

7 days

2.62 1048.0 16630 (Milheiro et al. 2014)

Pd-Ag (Orion Argos)



7 days

0.05 20.0 317 (Milheiro et al. 2014)

Amalgam (Tytin (Kerr UK)

discs Ø 10mm x2mm

0% H2O2 1% H2O2 20ml

24 hrs 0.08 0.38

9.2 41.6

146 660

(Al-Salehi et al. 2007)

Zn Au-Pt based (a.o. Biocclus 4®)

cast alloy specimen plate 10x10x0.5mm

H2O Sprite light®; pH 2.8 20ml

2 hrs

0.733 4.0

80.6 440.0

1240 6769

(Johnson et al. 2010)

Pd Pd-Cu (Orion Vesta)



7 days

0.67 276.0 2.594 (Milheiro et al. 2014)

Pd-Ag

(Orion Argos) cast alloy specimen 2.06cm2


7 days

0.33 136.0 1.278 (Milheiro et al. 2014)

Au Au-Pt based (Biocclus 4®)

cast alloy specimen 10x10x0.5mm

H2O Sprite light ®; pH2.8 20ml

2 hrs 0.019 0.136

1.9 15.0

9.64 76.15

(Johnson et al. 2010)

Hg Amalgam (Tytin (Kerr UK)

discs Ø 10mm x2mm

0% H2O2 1% H2O2 20ml

24 hrs 0.02 3.28

2.7 360.0

13.45 1791

(Al-Salehi et al. 2007)

a) Unless otherwise stated, experiments were performed with polished alloys, at 37o, and at a neutral pH b) References published from 2005 till 2015c) MEM: Minimal Essential Mediumd) n.d.: not detectable


5

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